In the wireless communication system, the sending end and the receiving end use a plurality of antennas with the space multiplexing mode to obtain a higher speed. Compared to the general space multiplexing method, a kind of enhanced technology is that the receiving end feeds back the channel information to the sending end, and the sending end uses the some transmission precoding technologies according to the obtained channel information to greatly improve the transmission performance. As for the single user multi-input multi-output (MIMO), it uses the channel feature vector information to perform the precoding directly; as for the multi-user MIMO, it needs more accurate channel information.
In the long term evolution (LTE) plan, for the feedback of the channel information, a feedback method which utilizes a simple single codebook is mainly used, and the performance of transmitting precoding technical in the MIMO depends more on the accuracy of the codebook feedback therein.
Here the basic principle of the channel information quantization feedback based on the codebook is described briefly as follows:
Suppose that the limited feedback channel capacity is B bps/Hz, and then the number of available code words is N=2B. The feature vector space of the channel matrix forms the codebook space at ={F1, F2 . . . FN} through the quantization. The transmitting end and the receiving end both keep or produce in real time that codebook (which is the same in both the receiving end and the sending end). According to the channel matrix H obtained by the receiving end, the receiving end selects one code word {circumflex over (F)} which is most matched with the channel from the  according to a certain criterion, and feeds back the sequence number of code word i to the transmitting end. Here, the sequence number of code word is called precoding matrix indicator (PMI). The transmitting end finds the corresponding precoding code word {circumflex over (F)} according to that sequence number i, thus obtaining the channel information, and {circumflex over (F)} represents the feature vector information of the channel.
Generally speaking,  can be divided as a codebook corresponding to a plurality of Ranks, each Rank would correspond to a plurality of code words to quantize the precoding matrix formed by the channel feature vector under the Rank. Since the number of the Ranks and the number the non-zero feature vectors of the channel are equal, generally speaking, the code words with the Rank being N will have N columns. So, the codebook  can be divided into a plurality of sub codebooks with respect to different Ranks, as shown in Table 1.
TABLE 1 Layer number υ(Rank)12. . .N 1 2. . . NCode word vectorCode word matrixCode word matrixset with the columnset with theset with thenumber being 1column numbercolumn number being 2being N
Wherein, the code words needing to be stored when Rank>1 are all in matrix form, wherein, the codebook in the LTE protocol adopts this kind of feedback method of codebook quantization. The codebook of the LTE downlink 4 transmission antennas is show in Table 2, and actually in the LTE, the meaning of the precoding codebook is same with that of the channel information quantization codebook. For unifying hereinafter, the vectors can be regarded as a matrix with the dimension being 1.
TABLE 2Code wordTotal layer number     (RI)indexun12340u0 = [1 −1 −1 −1]TW0(1)W0(14)/2W0(124)/{square root over (3)}W0(1234)/21u1 = [1 −j 1 j]TW1(1)W1(12)/2W1(123)/{square root over (3)}W1(1234)/22u2 = [1 1 −1 1]TW2(1)W2(12)/2W2(123)/{square root over (3)}W2(3214)/23u3 = [1 j 1 −j]TW3(1)W3(12)/2W3(123)/{square root over (3)}W3(3214)/24u4 = [1 (−1 − j)/{square root over (2)} −j (1 − j)/{square root over (2)}]TW4(1)W4(14)/2W4(124)/{square root over (3)}W4(1234)/25u5 = [1 (1 − j)/{square root over (2)} j (−1 − j)/{square root over (2)}]TW5(1)W5(14)/2W5(124)/{square root over (3)}W5(1234)/26u6 = [1 (1 + j)/{square root over (2)} −j (−1 + j)/{square root over (2)}]TW6(1)W6(13)/2W6(134)/{square root over (3)}W6(1324)/27u7 = [1 (−1 + j)/{square root over (2)} j (1 + j)/{square root over (2)}]TW7(1)W7(13)/2W7(134)/{square root over (3)}W7(1324)/28u8 = [1 −1 1 1]TW8(1)W8(12)/2W8(124)/{square root over (3)}W8(1234)/29u9 = [1 −j −1 −j]TW9(1)W9(14)/2W9(134)/{square root over (3)}W9(1234)/210u10 = [1 1 1 −1]TW10(1)W10(13)/2W10(123)/{square root over (3)}W10(1324)/211u11 = [1 j −1 j]TW11(1)W11(13)/2W11(134)/{square root over (3)}W11(1324)/212u12 = [1 −1 −1 1]TW12(1)W12(12)/2W12(123)/{square root over (3)}W12(1234)/213u13 = [1 −1 1 −1]TW13(1)W13(13)/2W13(123)/{square root over (3)}W13(1324)/214u14 = [1 1 −1 −1]TW14(1)W14(13)/2W14(123)/{square root over (3)}W14(3214)/215u15 = [1 1 1 1]TW15(1)W15(12)/2W15(123)/{square root over (3)}W15(1234)/2
Wherein, Wn=I−2ununH/unHun, I is a unit matrix, Wk(j) represents the j column vector of the matrix Wk. Wk(j1, j2, . . . jn) represents the matrix formed by the j1, j2, . . . , jn columns of the matrix Wk.
All of the above description is the principle of the codebook feedback technology in the LTE, and when implementing, it will also involve some specific feedback methods.
The feedback granularity of the channel information is introduced firstly. In the LTE standard, the minimum feedback unit of the channel information is the Subband channel information. One Subband is composed of several resource blocks (RB), and each RB is composed of a plurality of resource elements (RE). The RE is the minimum unit of the time-frequency resource in the LTE, and the resource representation way of the LTE continues to be used in the LTE-A. Several Subbands can be called Multi-Subband, and a plurality of Subbands can be called Wideband.
Now the feedback content corresponding to the channel information in the LTE is introduced, and the channel status information feedback includes: channel quality indication (abbreviated as CQI) information, PMI and rank indicant (abbreviated as RI). Here, the CSI content which we pay most attention to is the PMI information, but the RI and the CQI all belong to the content of the channel status information feedback.
The CQI is an index for weighing the quality of the downlink channel. The CQI is represented by the integer value of 0-15 in the 36-213 protocol, which respectively represents different CQI grades, and different CQIs correspond to their own modulation schemes and coding rates (modulation and coding scheme, MCS).
The RI is used for describing the number of the independent channels of the space, which corresponds to the rank of the channel response matrix. In the mode of open loop space multiplexing and closed loop space multiplexing, the UE is required to feed back the RI info illation, and it does not need to feed back the RI information in other modes. The rank of the channel matrix corresponds to the layer number.
Then some mechanisms related to the channel information feedback in the LTE are described:
The feedback modes of the uplink channel information in the LTE are divided into two kinds: the periodic channel information feedback on the physical uplink control channel (PUCCH) and the aperiodic channel information feedback on the physical uplink data shared channel (PUSCH). The PUCCH is a control channel, the reliability of the feedback is higher, but its feedback resources are more valuable, and the feedback overhead is limited strictly. Generally the feedback quantity of CSI (including one or more kinds of the PMI, the CQI and the RI) of one time cannot exceed 11 bits. The PUSCH can provide more CSI feedback resources, but the reliability cannot be guaranteed, and since the data transmission resources need to be occupied, and the data service transmission would be affected.
The long term evolution advanced (LTE-A) system, as the evolved standard of the LTE, supports greater system bandwidth (reaching as high as 100 MHz), and the LTE current standard is backwards compatible. In order to obtain much higher average spectral efficiency of the cell and improve the marginal coverage and throughput of the cell, the LTE-A supports at most 8 antennas in downlink on the basis of the current LTE system, and provides some feedback enhanced technologies with respect to the codebook feedback, which is mainly to strengthen the feedback precision of the codebook and compress the overhead by using the time relativity and/or the frequency domain relativity of the channel information. This technology can improve the frequency spectrum utilization rate of the international mobile telecommunications-advance (IMT-Advance) system and relieve the short supply of the spectral resources. Meanwhile, considering that the main application of 8 antennas will be the situation of bipolar, the design and enhancement of the codebook needs to fully consider the feature of the bipolar channel.
The main idea of this kind of the feedback technology of the enhanced codebook is to increase the overhead of the PMI feedback compared to the LTE feedback, and together represent the status information of the channel by using the feedback of two PMIS, mainly including two kinds of implementation modes:
the dual codebooks and dual PMI feedbacks are defined, or the single codebook equivalent to the dual codebooks and the dual PMI feedbacks are defined.
Defining dual codebooks and dual PMI feedbacks can further be described as:
1) the preceding/feedback structure of one Subband is composed of two matrixes.
2) each of the two matrixes belongs to one individual codebook. The codebook is known in advance at the same time by the base station and the UE. The feedback code word can be changed at different time and different Subbands.
3) one matrix represents the attribute of the long-time channel or the bandwidth. Another matrix represents the attribute of the short-time channel or a certain frequency band.
4) the used matrix codebooks are represented by a limited number of matrix sets, and each matrix is knowable for the UE and the base station.
5) wherein, one matrix can be a stationary matrix, and does not need the feedback. This moment, it corresponds to the case of degenerating to the single codebook feedback (which may be used in the case of unrelated channel of the high rank and the low rank).
It can be seen from here, a kind of structure based on the dual codebooks is provided with respect to the feedback of the channel information, which can be further described as:
for one or a plurality of union Subbands needing to feed back the channel information, the UE feeds back two PMI information (in some situations, it might not be through the feedback, one PMI also can be predefined as a fixed value without feedback), which are PMI1 and PMI2 respectively, to the base station, wherein, the PMI1 corresponds to the code word W1 in one codebook C1, and the PMI2 corresponds to the code word W2 in another codebook C2. The base station has the same information of C1 and C2, after receiving the PMI1 and the PMI2, it finds the corresponding code words W1 and W2 from the corresponding codebooks C1 and C2, and calculates W=F(W1, W2) to obtain the channel information W according to the agreed function rule F.
The above dual codebooks design criteria is a kind of specific codebook format in the LTE-A. In a specific implementation, it only needs to define the codebook corresponding to the W1 and the W2, but actually there is a virtual codebook corresponding to W, and the consideration on performance aspect in the design is based on the codebook corresponding to W. The design of the codebook feedback has two important parts, the first important part is the specific structure, overhead and specific code word of the W, which concerns the performance of the dual codebooks feedback directly (although the feedback format of the specific definition is to feed back the W1 and the W2 without directly feeding back the W), and the consideration for this part is similar for the formats of the single codebook and the dual codebooks. The second important part is about how to divide the W into 2 codebooks to represent that the characteristic of the time domain/frequency domain of the channel changing can be more adapted, and the overhead is saved effectively. This belongs to the consideration for saving the overhead of the dual codebooks, and there is no consideration in this respect for the single codebook.
Except the above dual codebooks implementation, also there is one kind of single codebook feedback mode which is equivalent to using the dual codebooks and dual PMIs feedback: to define the single codebook equivalent to the dual codebooks and the dual PMIs feedback.
As to Rank=r, r is an integer, and the difference from the above 4Tx codebook lies in that, when the single codebook equivalent to the dual codebooks is used, it needs 2 PMI feedbacks to represent its information to feedback the code word in the corresponding codebook. The single codebook equivalent to the dual codebooks can generally be represented as shown in below Table 3.
TABLE 3i201. . .N2i10Wi1, i2Wi1, i2Wi1, i2Wi1, i21Wi1, i2Wi1, i2Wi1, i2Wi1, i22Wi1, i2Wi1, i2Wi1, i2Wi1, i23Wi1, i2Wi1, i2Wi1, i2Wi1, i2. . .Wi1, i2Wi1, i2Wi1, i2Wi1, i2N-1Wi1, i2Wi1, i2Wi1, i2Wi1, i2N1Wi1, i2Wi1, i2Wi1, i2Wi1, i2
Here, Wi1,i2 is one code word indicated by i1 i2 together, and generally can be expressed as the function format W(i1, i2), and only i1 i2 need to be determined.
For example, when r=1,φnejπm/2 vm=[1ej2πm/32ej4πm/32ej6πm/32]T
TABLE 4i2i1012345670-15W2i1,0(1)W2i1,1(1)W2i1,2(1)W2i1,3(1)W2i1+1,0(1)W2i1+1,1(1)W2i1+1,2(1)W2i1+1,3(1)i2i1891011121314150-15W2i1+2,0(1)W2i1+2,1(1)W2i1+2,2(1)W2i1+2,3(1)W2i1+3,0(1)W2i1+3,1(1)W2i1+3,2(1)W2i1+3,3(1)      where    ⁢                  ⁢          W              m        ,        n                    (        1        )              =            1              8              ⁡          [                                                  v              m                                                                                          φ                n                            ⁢                              v                m                                                        ]      
Actually this mode is equivalent to the dual codebooks and dual PMNs, and the only difference lies in that this method does not define the two codebooks C1 and C2 any more, instead, defining the dual codebooks and the codebook corresponding to the W formed by the function relationship of the dual codebooks, that is, the virtual codebook are replaced by the actually defining the C1 and C2.
Since in the LTE-A, the precision of the feedback is strengthened, which makes the sum of the overhead required by feeding back the information of the PMI1 and the PMI2 (also can be interpreted as the overhead of the codebook corresponding to the W) increase to some extent relative to the overhead of the single codebook in the LTE. when that codebook is applied to the channel information feedback on the PUCCH, and when the W1 and the W2 are transmitted in a subframe at the same time, it will make the CSI feedback overhead of the PUCCH be over the 11-bit overhead limitation, thus making the transmission performance of the PUCCH drop seriously and causing very severe influence on the system.
In addition, even if the PMI1 and the PMI2 are transmitted separately, for example, the PMI1 and the RI are transmitted together, although the feedback of the PMI1+RI is not over the 11-bit overhead limitation, since increasing the overhead will make the bit error rate rise in the case that the transmission resources are definite, the bit error rate of the RI cannot be guaranteed very well, there will be the problem that the bit error rate of the RI does not meet the requirement. When the PMI2 and the CQI are transmitted together, the excessive overhead also will cause the bit error rate increase and affect system performance.
No matter being the single codebook or the dual codebooks feedback, the increase of the feedback overhead will make the feedback overhead of the PUCCH be over the limitation, and make its transmission performance drop seriously. This is the problem required to be solved in the related art.